A three-phase inverter supplying a load, especially in application areas such as, an uninterruptable power supply (UPS) is known in the art. If the load is balanced, a variety of control methods may be utilized to regulate a three-phase output voltage of the three-phase inverter. For example, the three-phase output voltage of the three-phase inverter supplying a balanced load may be regulated by use of one or more stationary frame proportional-integral (PI) controllers.
However, it is difficult to regulate the three-phase output voltage of the three-phase inverter by use of the one or more stationary frame PI controllers, when the three-phase inverter is supplying an unbalanced load. This is because the integral pails in atypical stationary frame PI controller are not able to compensate the effect of the unbalanced load. For example, the three-phase output voltage of the three-phase inverter across the unbalanced load is unbalanced due to undesired negative and zero sequence components of the three-phase output voltage. The negative sequence component is a stable component that can be eliminated by using the stationary frame PI controller. However, the stationary frame PI controller cannot eliminate the zero sequence component since it is a variable component. Thus, eliminating the zero sequence component in the three-phase output voltage of the three-phase inverter is difficult by using the stationary frame PI controller.
U.S. Pat. No. 5,883,796 discloses a method and apparatus for the dynamic series voltage restoration for sensitive loads in unbalanced power systems. is a recovery system for the unbalanced loads generated by faults in an existing balanced load system. This system introduce a compensator inverter that generates an inverter voltage signal in series with the power transmission line, which restores the positive sequence load voltage component to pre-fault conditions, and which cancels the negative and the zero sequence components of the load voltage signal. This system does not provide solution for the scenario where the three-phase inverter is feeding the unbalanced load.
Given description covers one or more problems existing in the art and discloses a method to solve the problem(s).